While it seems religious in nature, all of this stems from politics. Way back when, the Middle East was one big area with smaller parts under control of various tribal leaders. Then came oil and we carved up the countries based on the oil. This fractured the cultural community and it's never resolving because of those issues. And it was politics that carved up the land into countries.
IS (as they call themselves now) are also killing muslim journalists left and right, we just don't hear of them here in our western world. They want total control of what is put out there and they can't do that with journalists around. If this really were religious, they wouldn't be killing Muslims indiscriminately.